[alg.is.permutation] Rephrase to simplify (#4071)

Defines "last2" and "pred" for the overloads with no such parameters
so the remainder of the specification need not exhaustively describe
each case.

Author: CaseyCarter

source/algorithms.tex

@@ -3965,6 +3965,11 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{last2} be \tcode{first2 + (last1 - first1)}
+for the overloads with no parameter named \tcode{last2},
+and let \tcode{pred} be \tcode{equal_to\{\}}
+for the overloads with no parameter \tcode{pred}.
 
 \pnum
 \mandates
@@ -3974,20 +3979,14 @@
 \expects
 The comparison function is an equivalence relation.
 
-\pnum
-\remarks
-If \tcode{last2} was not given in the argument list,
-it denotes \tcode{first2 + (last1 - first1)} below.
-
 \pnum
 \returns
 If \tcode{last1 - first1 != last2 - first2}, return \tcode{false}.
 Otherwise return \tcode{true}
 if there exists a permutation of the elements
-in the range \range{first2}{first2 + (last1 - first1)},
+in the range \range{first2}{last2},
 beginning with \tcode{ForwardIterator2 begin},
-such that \tcode{equal(first1, last1, begin)} returns \tcode{true} or
-\tcode{equal(first1, last1, begin, pred)} returns \tcode{true};
+such that \tcode{equal(first1, last1, begin, pred)} returns \tcode{true};
 otherwise, returns \tcode{false}.
 
 \pnum
@@ -3998,10 +3997,7 @@
 \tcode{last1 - first1 != last2 - first2}.
 Otherwise, exactly \tcode{last1 - first1} applications
 of the corresponding predicate
-if \tcode{equal(\brk{}first1, last1, first2, last2)} would return \tcode{true}
-if \tcode{pred} was not given in the argument list or
-\tcode{equal(first1, last1, first2, last2, pred)} would return \tcode{true}
-if \tcode{pred} was given in the argument list;
+if \tcode{equal(first1, last1, first2, last2, pred)} would return \tcode{true};
 otherwise, at worst \bigoh{N^2}, where $N$ has the value \tcode{last1 - first1}.
 \end{itemdescr}