Changeset 29c9b23
- Timestamp:
- Feb 4, 2021, 9:56:11 AM (4 years ago)
- Branches:
- ADT, arm-eh, ast-experimental, enum, forall-pointer-decay, jacob/cs343-translation, master, new-ast-unique-expr, pthread-emulation, qualifiedEnum
- Children:
- 9af0fe2d
- Parents:
- 6a99803
- Location:
- doc/theses/andrew_beach_MMath
- Files:
-
- 5 edited
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doc/theses/andrew_beach_MMath/existing.tex
r6a99803 r29c9b23 1 \chapter{\ texorpdfstring{\CFA Existing Features}{Cforall Existing Features}}1 \chapter{\CFA Existing Features} 2 2 3 3 \CFA (C-for-all)~\cite{Cforall} is an open-source project extending ISO C with … … 43 43 44 44 \section{Reference Type} 45 \CFA adds a rebindable reference type to C, but more expressive than the \C C45 \CFA adds a rebindable reference type to C, but more expressive than the \Cpp 46 46 reference. Multi-level references are allowed and act like auto-dereferenced 47 47 pointers using the ampersand (@&@) instead of the pointer asterisk (@*@). \CFA … … 60 60 61 61 Both constructors and destructors are operators, which means they are just 62 functions with special operator names rather than type names in \C C. The62 functions with special operator names rather than type names in \Cpp. The 63 63 special operator names may be used to call the functions explicitly (not 64 allowed in \C Cfor constructors).64 allowed in \Cpp for constructors). 65 65 66 66 In general, operator names in \CFA are constructed by bracketing an operator … … 89 89 matching overloaded destructor @void ^?{}(T &);@ is called. Without explicit 90 90 definition, \CFA creates a default and copy constructor, destructor and 91 assignment (like \C C). It is possible to define constructors/destructors for91 assignment (like \Cpp). It is possible to define constructors/destructors for 92 92 basic and existing types. 93 93 … … 95 95 \CFA uses parametric polymorphism to create functions and types that are 96 96 defined over multiple types. \CFA polymorphic declarations serve the same role 97 as \C Ctemplates or Java generics. The ``parametric'' means the polymorphism is97 as \Cpp templates or Java generics. The ``parametric'' means the polymorphism is 98 98 accomplished by passing argument operations to associate \emph{parameters} at 99 99 the call site, and these parameters are used in the function to differentiate … … 135 135 136 136 Note, a function named @do_once@ is not required in the scope of @do_twice@ to 137 compile it, unlike \C Ctemplate expansion. Furthermore, call-site inferencing137 compile it, unlike \Cpp template expansion. Furthermore, call-site inferencing 138 138 allows local replacement of the most specific parametric functions needs for a 139 139 call. … … 179 179 } 180 180 \end{cfa} 181 The generic type @node(T)@ is an example of a polymorphic-type usage. Like \C C181 The generic type @node(T)@ is an example of a polymorphic-type usage. Like \Cpp 182 182 templates usage, a polymorphic-type usage must specify a type parameter. 183 183 -
doc/theses/andrew_beach_MMath/features.tex
r6a99803 r29c9b23 5 5 6 6 \section{Virtuals} 7 Virtual types and casts are not part of the exception system nor are they 8 required for an exception system. But an object-oriented style hierarchy is a 9 great way of organizing exceptions so a minimal virtual system has been added 10 to \CFA. 11 12 The pattern of a simple hierarchy was borrowed from object-oriented 13 programming was chosen for several reasons. 14 The first is that it allows new exceptions to be added in user code 15 and in libraries independently of each other. Another is it allows for 16 different levels of exception grouping (all exceptions, all IO exceptions or 17 a particular IO exception). Also it also provides a simple way of passing 18 data back and forth across the throw. 19 7 20 Virtual types and casts are not required for a basic exception-system but are 8 21 useful for advanced exception features. However, \CFA is not object-oriented so 9 22 there is no obvious concept of virtuals. Hence, to create advanced exception 10 features for this work, I needed to design ed and implementeda virtual-like23 features for this work, I needed to design and implement a virtual-like 11 24 system for \CFA. 12 25 26 % NOTE: Maybe we should but less of the rational here. 13 27 Object-oriented languages often organized exceptions into a simple hierarchy, 14 28 \eg Java. … … 61 75 While much of the virtual infrastructure is created, it is currently only used 62 76 internally for exception handling. The only user-level feature is the virtual 63 cast, which is the same as the \C C\lstinline[language=C++]|dynamic_cast|.77 cast, which is the same as the \Cpp \lstinline[language=C++]|dynamic_cast|. 64 78 \label{p:VirtualCast} 65 79 \begin{cfa} 66 80 (virtual TYPE)EXPRESSION 67 81 \end{cfa} 68 Note, the syntax and semantics matches a C-cast, rather than the unusual \CC 69 syntax for special casts. Both the type of @EXPRESSION@ and @TYPE@ must be a 70 pointer to a virtual type. The cast dynamically checks if the @EXPRESSION@ type 71 is the same or a subtype of @TYPE@, and if true, returns a pointer to the 82 Note, the syntax and semantics matches a C-cast, rather than the function-like 83 \Cpp syntax for special casts. Both the type of @EXPRESSION@ and @TYPE@ must be 84 a pointer to a virtual type. 85 The cast dynamically checks if the @EXPRESSION@ type is the same or a subtype 86 of @TYPE@, and if true, returns a pointer to the 72 87 @EXPRESSION@ object, otherwise it returns @0p@ (null pointer). 73 88 … … 82 97 \begin{cfa} 83 98 trait is_exception(exceptT &, virtualT &) { 84 virtualT const & @get_exception_vtable@(exceptT *);99 virtualT const & get_exception_vtable(exceptT *); 85 100 }; 86 101 \end{cfa} 87 The function takes any pointer, including the null pointer, and returns a 88 reference to the virtual-table object. Defining this function also establishes 89 the virtual type and a virtual-table pair to the \CFA type-resolver and 90 promises @exceptT@ is a virtual type and a child of the base exception-type. 91 92 \PAB{I do not understand this paragraph.} 93 One odd thing about @get_exception_vtable@ is that it should always be a 94 constant function, returning the same value regardless of its argument. A 95 pointer or reference to the virtual table instance could be used instead, 96 however using a function has some ease of implementation advantages and allows 97 for easier disambiguation because the virtual type name (or the address of an 98 instance that is in scope) can be used instead of the mangled virtual table 99 name. Also note the use of the word ``promise'' in the trait 100 description. Currently, \CFA cannot check to see if either @exceptT@ or 101 @virtualT@ match the layout requirements. This is considered part of 102 @get_exception_vtable@'s correct implementation. 102 The trait is defined over two types, the exception type and the virtual table 103 type. This should be one-to-one, each exception type has only one virtual 104 table type and vice versa. The only assertion in the trait is 105 @get_exception_vtable@, which takes a pointer of the exception type and 106 returns a reference to the virtual table type instance. 107 108 The function @get_exception_vtable@ is actually a constant function. 109 Recardless of the value passed in (including the null pointer) it should 110 return a reference to the virtual table instance for that type. 111 The reason it is a function instead of a constant is that it make type 112 annotations easier to write as you can use the exception type instead of the 113 virtual table type; which usually has a mangled name. 114 % Also \CFA's trait system handles functions better than constants and doing 115 % it this way 116 117 % I did have a note about how it is the programmer's responsibility to make 118 % sure the function is implemented correctly. But this is true of every 119 % similar system I know of (except Agda's I guess) so I took it out. 103 120 104 121 \section{Raise} … … 109 126 trait is_termination_exception( 110 127 exceptT &, virtualT & | is_exception(exceptT, virtualT)) { 111 void @defaultTerminationHandler@(exceptT &);128 void defaultTerminationHandler(exceptT &); 112 129 }; 113 130 \end{cfa} … … 119 136 trait is_resumption_exception( 120 137 exceptT &, virtualT & | is_exception(exceptT, virtualT)) { 121 void @defaultResumptionHandler@(exceptT &);138 void defaultResumptionHandler(exceptT &); 122 139 }; 123 140 \end{cfa} … … 126 143 127 144 Finally there are three convenience macros for referring to the these traits: 128 @IS_EXCEPTION@, @IS_TERMINATION_EXCEPTION@ and @IS_RESUMPTION_EXCEPTION@. Each 129 takes the virtual type's name, and for polymorphic types only, the 130 parenthesized list of polymorphic arguments. These macros do the name mangling 131 to get the virtual-table name and provide the arguments to both sides 132 \PAB{What's a ``side''?} 145 @IS_EXCEPTION@, @IS_TERMINATION_EXCEPTION@ and @IS_RESUMPTION_EXCEPTION@. 146 All three traits are hard to use while naming the virtual table as it has an 147 internal mangled name. These macros take the exception name as their first 148 argument and do the mangling. They all take a second argument for polymorphic 149 types which is the parenthesized list of polymorphic arguments. These 150 arguments are passed to both the exception type and the virtual table type as 151 the arguments do have to match. 152 153 For example consider a function that is polymorphic over types that have a 154 defined arithmetic exception: 155 \begin{cfa} 156 forall(Num | IS_EXCEPTION(Arithmetic, (Num))) 157 void some_math_function(Num & left, Num & right); 158 \end{cfa} 133 159 134 160 \subsection{Termination} … … 147 173 throw EXPRESSION; 148 174 \end{cfa} 149 The expression must return a termination-exception reference, where the 150 termination exception has a type with a @void defaultTerminationHandler(T &)@ 151 (default handler) defined. The handler is found at the call site using \CFA's 152 trait system and passed into the exception system along with the exception 153 itself. 154 155 At runtime, a representation of the exception type and an instance of the 156 exception type is copied into managed memory (heap) to ensure it remains in 175 The expression must return a reference to a termination exception, where the 176 termination exception is any type that satifies @is_termination_exception@ 177 at the call site. 178 Through \CFA's trait system the functions in the traits are passed into the 179 throw code. A new @defaultTerminationHandler@ can be defined in any scope to 180 change the throw's behavior (see below). 181 182 At runtime, the exception returned by the expression 183 is copied into managed memory (heap) to ensure it remains in 157 184 scope during unwinding. It is the user's responsibility to ensure the original 158 185 exception object at the throw is freed when it goes out of scope. Being … … 166 193 try { 167 194 GUARDED_BLOCK 168 } @catch (EXCEPTION_TYPE$\(_1\)$ * NAME)@{ // termination handler 1195 } catch (EXCEPTION_TYPE$\(_1\)$ * NAME$\(_1\)$) { // termination handler 1 169 196 HANDLER_BLOCK$\(_1\)$ 170 } @catch (EXCEPTION_TYPE$\(_2\)$ * NAME)@{ // termination handler 2197 } catch (EXCEPTION_TYPE$\(_2\)$ * NAME$\(_2\)$) { // termination handler 2 171 198 HANDLER_BLOCK$\(_2\)$ 172 199 } … … 179 206 Exception matching checks the representation of the thrown exception-type is 180 207 the same or a descendant type of the exception types in the handler clauses. If 181 there is a match, a pointer to the exception object created at the throwis182 bound to @NAME@ and the statements in the associated @HANDLER_BLOCK@ are183 executed. If control reaches the end of the handler, the exception is freed, 184 and control continues after the try statement.208 it is the same of a descendent of @EXCEPTION_TYPE@$_i$ then @NAME@$_i$ is 209 bound to a pointer to the exception and the statements in @HANDLER_BLOCK@$_i$ 210 are executed. If control reaches the end of the handler, the exception is 211 freed and control continues after the try statement. 185 212 186 213 The default handler visible at the throw statement is used if no matching 187 214 termination handler is found after the entire stack is searched. At that point, 188 215 the default handler is called with a reference to the exception object 189 generated at the throw. If the default handler returns, the system default190 action is executed, which often terminates the program. This feature allows216 generated at the throw. If the default handler returns, control continues 217 from after the throw statement. This feature allows 191 218 each exception type to define its own action, such as printing an informative 192 219 error message, when an exception is not handled in the program. 220 However the default handler for all exception types triggers a cancellation 221 using the exception. 193 222 194 223 \subsection{Resumption} … … 197 226 Resumption raise, called ``resume'', is as old as termination 198 227 raise~\cite{Goodenough75} but is less popular. In many ways, resumption is 199 simpler and easier to understand, as it is simply a dynamic call (as in200 Lisp).The semantics of resumption is: search the stack for a matching handler,228 simpler and easier to understand, as it is simply a dynamic call. 229 The semantics of resumption is: search the stack for a matching handler, 201 230 execute the handler, and continue execution after the resume. Notice, the stack 202 231 cannot be unwound because execution returns to the raise point. Resumption is … … 210 239 \end{cfa} 211 240 The semantics of the @throwResume@ statement are like the @throw@, but the 212 expression has a type with a @void defaultResumptionHandler(T &)@ (default 213 handler) defined, where the handler is found at the call site by the type 214 system. At runtime, a representation of the exception type and an instance of 215 the exception type is \emph{not} copied because the stack is maintained during 216 the handler search. 241 expression has return a reference a type that satifies the trait 242 @is_resumption_exception@. Like with termination the exception system can 243 use these assertions while (throwing/raising/handling) the exception. 244 245 At runtime, no copies are made. As the stack is not unwound the exception and 246 any values on the stack will remain in scope while the resumption is handled. 217 247 218 248 Then the exception system searches the stack starting from the resume and 219 proceeding to wardsthe base of the stack, from callee to caller. At each stack249 proceeding to the base of the stack, from callee to caller. At each stack 220 250 frame, a check is made for resumption handlers defined by the @catchResume@ 221 251 clauses of a @try@ statement. … … 223 253 try { 224 254 GUARDED_BLOCK 225 } @catchResume (EXCEPTION_TYPE$\(_1\)$ * NAME)@ { // resumption handler 1255 } catchResume (EXCEPTION_TYPE$\(_1\)$ * NAME$\(_1\)$) { 226 256 HANDLER_BLOCK$\(_1\)$ 227 } @catchResume (EXCEPTION_TYPE$\(_2\)$ * NAME)@ { // resumption handler 2257 } catchResume (EXCEPTION_TYPE$\(_2\)$ * NAME$\(_2\)$) { 228 258 HANDLER_BLOCK$\(_2\)$ 229 259 } … … 254 284 current point on the stack because new try statements may have been pushed by 255 285 the handler or functions called from the handler. If there is no match back to 256 the point of the current handler, the search skips\label{p:searchskip} the stack frames already257 s earched by the first resume and continues after the try statement. The default258 handler always continues from default handler associated with the point where 259 the exception is created.286 the point of the current handler, the search skips\label{p:searchskip} the 287 stack frames already searched by the first resume and continues after 288 the try statement. The default handler always continues from default 289 handler associated with the point where the exception is created. 260 290 261 291 % This might need a diagram. But it is an important part of the justification … … 276 306 \end{verbatim} 277 307 278 This resumption search-pattern reflect the one for termination, which matches 279 with programmer expectations. However, it avoids the \emph{recursive 280 resumption} problem. If parts of the stack are searched multiple times, loops 308 This resumption search pattern reflects the one for termination, and so 309 should come naturally to most programmers. 310 However, it avoids the \emph{recursive resumption} problem. 311 If parts of the stack are searched multiple times, loops 281 312 can easily form resulting in infinite recursion. 282 313 … … 284 315 \begin{cfa} 285 316 try { 286 throwResume$\(_1\)$ (E &){}; 287 } catch( E * ) { 288 throwResume; 289 } 290 \end{cfa} 291 Based on termination semantics, programmer expectation is for the re-resume to 292 continue searching the stack frames after the try statement. However, the 293 current try statement is still on the stack below the handler issuing the 294 reresume \see{\VRef{s:Reraise}}. Hence, the try statement catches the re-raise 295 again and does another re-raise \emph{ad infinitum}, which is confusing and 296 difficult to debug. The \CFA resumption search-pattern skips the try statement 297 so the reresume search continues after the try, mathcing programmer 298 expectation. 317 throwResume (E &){}; // first 318 } catchResume(E *) { 319 throwResume (E &){}; // second 320 } 321 \end{cfa} 322 If this handler is ever used it will be placed on top of the stack above the 323 try statement. If the stack was not masked than the @throwResume@ in the 324 handler would always be caught by the handler, leading to an infinite loop. 325 Masking avoids this problem and other more complex versions of it involving 326 multiple handlers and exception types. 327 328 Other masking stratagies could be used; such as masking the handlers that 329 have caught an exception. This one was choosen because it creates a symmetry 330 with termination (masked sections of the stack would be unwound with 331 termination) and having only one pattern to learn is easier. 299 332 300 333 \section{Conditional Catch} 301 Both termination and resumption handler-clauses may perform conditional matching: 334 Both termination and resumption handler clauses can be given an additional 335 condition to further control which exceptions they handle: 302 336 \begin{cfa} 303 337 catch (EXCEPTION_TYPE * NAME ; @CONDITION@) … … 323 357 324 358 \section{Reraise} 359 \color{red}{From Andrew: I recomend we talk about why the language doesn't 360 have rethrows/reraises instead.} 361 325 362 \label{s:Reraise} 326 363 Within the handler block or functions called from the handler block, it is … … 328 365 @throwResume@, respective. 329 366 \begin{cfa} 330 catch( ... ) { 367 try { 368 ... 369 } catch( ... ) { 331 370 ... throw; // rethrow 332 371 } catchResume( ... ) { … … 341 380 handler is generated that does a program-level abort. 342 381 343 344 382 \section{Finally Clauses} 345 383 A @finally@ clause may be placed at the end of a @try@ statement. … … 347 385 try { 348 386 GUARDED_BLOCK 349 } ... 350 }finally {387 } ... // any number or kind of handler clauses 388 ... finally { 351 389 FINALLY_BLOCK 352 390 } 353 391 \end{cfa} 354 The @FINALLY_BLOCK@ is executed when the try statement is unwound from the 355 stack, \ie when the @GUARDED_BLOCK@ or any handler clause finishes. Hence, the 356 finally block is always executed. 392 The @FINALLY_BLOCK@ is executed when the try statement is removed from the 393 stack, including when the @GUARDED_BLOCK@ or any handler clause finishes or 394 during an unwind. 395 The only time the block is not executed is if the program is exited before 396 that happens. 357 397 358 398 Execution of the finally block should always finish, meaning control runs off … … 370 410 possible forwards the cancellation exception to a different stack. 371 411 412 Cancellation is not an exception operation like termination or resumption. 372 413 There is no special statement for starting a cancellation; instead the standard 373 414 library function @cancel_stack@ is called passing an exception. Unlike a … … 379 420 \item[Main Stack:] 380 421 The main stack is the one used by the program main at the start of execution, 381 and is the only stack in a sequential program. Hence, when cancellation is 382 forwarded to the main stack, there is no other forwarding stack, so after the 383 stack is unwound, there is a program-level abort. 422 and is the only stack in a sequential program. Even in a concurrent program 423 the main stack is only dependent on the environment that started the program. 424 Hence, when the main stack is cancelled there is nowhere else in the program 425 to notify. After the stack is unwound, there is a program-level abort. 384 426 385 427 \item[Thread Stack:] … … 387 429 @is_thread@ trait. A thread only has two points of communication that must 388 430 happen: start and join. As the thread must be running to perform a 389 cancellation, it must occur after start and before join, so join is a 390 cancellation point. After the stack is unwound, the thread halts and waits for 391 another thread to join with it. The joining thread, checks for a cancellation, 431 cancellation, it must occur after start and before join, so join is used 432 for communication here. 433 After the stack is unwound, the thread halts and waits for 434 another thread to join with it. The joining thread checks for a cancellation, 392 435 and if present, resumes exception @ThreadCancelled@. 393 436 … … 397 440 the exception is not caught. The implicit join does a program abort instead. 398 441 399 This semantics is for safety. One difficult problem for any exception system is 400 defining semantics when an exception is raised during an exception search: 401 which exception has priority, the original or new exception? No matter which 402 exception is selected, it is possible for the selected one to disrupt or 403 destroy the context required for the other. \PAB{I do not understand the 404 following sentences.} This loss of information can happen with join but as the 405 thread destructor is always run when the stack is being unwound and one 406 termination/cancellation is already active. Also since they are implicit they 407 are easier to forget about. 442 This semantics is for safety. If an unwind is triggered while another unwind 443 is underway only one of them can proceed as they both want to ``consume'' the 444 stack. Letting both try to proceed leads to very undefined behaviour. 445 Both termination and cancellation involve unwinding and, since the default 446 @defaultResumptionHandler@ preforms a termination that could more easily 447 happen in an implicate join inside a destructor. So there is an error message 448 and an abort instead. 449 450 The recommended way to avoid the abort is to handle the intial resumption 451 from the implicate join. If required you may put an explicate join inside a 452 finally clause to disable the check and use the local 453 @defaultResumptionHandler@ instead. 408 454 409 455 \item[Coroutine Stack:] A coroutine stack is created for a @coroutine@ object -
doc/theses/andrew_beach_MMath/future.tex
r6a99803 r29c9b23 10 10 \item 11 11 The implementation of termination is not portable because it includes 12 hand-crafted assembly statements. These sections must be generalized to support13 more hardware architectures, \egARM processor.12 hand-crafted assembly statements. These sections must be ported by hand to 13 support more hardware architectures, such as the ARM processor. 14 14 \item 15 15 Due to a type-system problem, the catch clause cannot bind the exception to a … … 24 24 scope of the @try@ statement, where the local control-flow transfers are 25 25 meaningful. 26 \item 27 There is no detection of colliding unwinds. It is possible for clean-up code 28 run during an unwind to trigger another unwind that escapes the clean-up code 29 itself; such as a termination exception caught further down the stack or a 30 cancellation. There do exist ways to handle this but currently they are not 31 even detected and the first unwind will simply be forgotten, often leaving 32 it in a bad state. 33 \item 34 Also the exception system did not have a lot of time to be tried and tested. 35 So just letting people use the exception system more will reveal new 36 quality of life upgrades that can be made with time. 26 37 \end{itemize} 27 38 -
doc/theses/andrew_beach_MMath/uw-ethesis-frontpgs.tex
r6a99803 r29c9b23 13 13 \vspace*{1.0cm} 14 14 15 \Huge 16 {\bf Exception Handling in \CFA} 15 {\Huge\bf Exception Handling in \CFA} 17 16 18 17 \vspace*{1.0cm} 19 18 20 \normalsize21 19 by \\ 22 20 23 21 \vspace*{1.0cm} 24 22 25 \Large 26 Andrew James Beach \\ 23 {\Large Andrew James Beach} \\ 27 24 28 25 \vspace*{3.0cm} 29 26 30 \normalsize31 27 A thesis \\ 32 28 presented to the University of Waterloo \\ … … 43 39 \vspace*{1.0cm} 44 40 45 \copyright \Andrew James Beach \the\year \\41 \copyright{} Andrew James Beach \the\year \\ 46 42 \end{center} 47 43 \end{titlepage} -
doc/theses/andrew_beach_MMath/uw-ethesis.tex
r6a99803 r29c9b23 70 70 % un-comment the second \documentclass line. 71 71 % 2) change the value assigned below to the boolean variable "PrintVersion" 72 % from " 72 % from "false" to "true". 73 73 74 74 % ====================================================================== … … 82 82 % one above: 83 83 %\documentclass[letterpaper,12pt,titlepage,openright,twoside,final]{book} 84 85 \usepackage{etoolbox} 84 86 85 87 % Some LaTeX commands I define for my own nomenclature. … … 105 107 % For including graphics N.B. pdftex graphics driver 106 108 \usepackage[pdftex]{graphicx} 109 % Removes large sections of the document. 110 \usepackage{comment} 107 111 108 112 % Hyperlinks make it very easy to navigate an electronic document. … … 201 205 \makeglossaries 202 206 203 \usepackage{comment}204 207 % cfa macros used in the document 205 208 %\usepackage{cfalab} 209 % I'm going to bring back eventually. 210 \makeatletter 211 % Combines all \CC* commands: 212 \newrobustcmd*\Cpp[1][\xspace]{\cfalab@Cpp#1} 213 \newcommand\cfalab@Cpp{C\kern-.1em\hbox{+\kern-.25em+}} 214 % Optional arguments do not work with pdf string. (Some fix-up required.) 215 \pdfstringdefDisableCommands{\def\Cpp{C++}} 216 \makeatother 217 206 218 \input{common} 207 \CFAStyle % CFA code-style for all languages 208 \lstset{language=CFA,basicstyle=\linespread{0.9}\tt} % CFA default lnaguage 219 % CFA code-style for all languages 220 \CFAStyle 221 % CFA default lnaguage 222 \lstset{language=CFA,basicstyle=\linespread{0.9}\tt} 223 % Annotations from Peter: 209 224 \newcommand{\PAB}[1]{{\color{blue}PAB: #1}} 225 % Change the style of abbreviations: 226 \renewcommand{\abbrevFont}{} 210 227 211 228 %======================================================================
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