Avoid name clashes with Sum and Product.

Fixes Github issue #62
#62

[Refactor]

Author: lemmy

modules/FiniteSetsExt.tla

@@ -13,7 +13,7 @@ FoldSet(op(_,_), base, set) ==
    (*************************************************************************)
    MapThenFoldSet(op, base, LAMBDA x : x, LAMBDA s : CHOOSE x \in s : TRUE, set)
 
-Sum(set) ==
+SumSet(set) ==
    (*************************************************************************)
    (* Calculate the sum of the elements in set.                             *)
    (*                                                                       *)
@@ -22,7 +22,7 @@ Sum(set) ==
    (*************************************************************************)
    FoldSet(+, 0, set)
 
-Product(set) ==
+ProductSet(set) ==
    (*************************************************************************)
    (* Calculuate the product of the elements in set.                        *)
    (*                                                                       *)

tests/FiniteSetsExtTests.tla

@@ -119,8 +119,8 @@ ASSUME SymDiff({1,2,3}, {2,3,4}) = {1,4}
 ASSUME SymDiff({1,2,3}, {2,3}) = {1}
 ASSUME SymDiff({2,3}, {2,3,4}) = {4}
 
-ASSUME Sum(1..3) = 6
-ASSUME Product(1..4) = 24
+ASSUME SumSet(1..3) = 6
+ASSUME ProductSet(1..4) = 24
 
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