2.7.3: Reification of lex_less constraints is broken

[informarte]

Consider this example:

include "lex_lesseq.mzn";

int: N = 10;
int: M = 10;

array [1..N] of var bool: x;
array [1..N] of var bool: y;

constraint lex_lesseq(x, y) \/ lex_lesseq(y, x);

solve satisfy;

output [
    "x = ", show(x), "\n",
    "y = ", show(y)]

MiniZinc 2.7.2 (with default backend) computes this solution:

x = [false, false, false, false, false, false, false, false, false, false]
y = [false, false, false, false, false, false, false, false, false, false]
----------

MiniZinc 2.7.3 prints an error message:

rror: flattening error: free variable in non-positive context
/home/informarte/Software/lib/MiniZincIDE-2.7.3-bundle-linux-x86_64/share/minizinc/std/fzn_lex_lesseq_bool_reif.mzn:9.3-41
  in binary '<->' operator expression
  in call 'lex_lesseq_std_decomposition'
/home/informarte/Software/lib/MiniZincIDE-2.7.3-bundle-linux-x86_64/share/minizinc/std/stdlib/stdlib_internal.mzn:1377.3-1396.7
  in if-then-else expression
/home/informarte/Software/lib/MiniZincIDE-2.7.3-bundle-linux-x86_64/share/minizinc/std/stdlib/stdlib_internal.mzn:1380.5-1395.13
  in let expression
/home/informarte/Software/lib/MiniZincIDE-2.7.3-bundle-linux-x86_64/share/minizinc/std/stdlib/stdlib_internal.mzn:1387.7-37
  in variable declaration for 'b'

[Dekker1]

Resolved by 1d35802