Module miscops 

Miscellaneous deterministic builtins: succ/2, plus/3, unify_with_occurs_check/2, write/1, writeln/1, nl/0.

Ported byte-for-byte from patch-prolog v1 (solver.rs arms, unify.rs occurs-check unifier). Notes:

• succ/2 both modes; succ(X, 0) fails; negatives raise domain_error(not_less_than_zero, _); both-unbound raises instantiation.
• plus/3 supports the three integer modes (any one argument unbound); fewer than two bound raises instantiation.
• unify_with_occurs_check/2 uses a LOCAL occurs-checking unifier (iterative; does not touch the shared unify.rs).
• write/1 / writeln/1 use v1’s term_to_string (infix operators, [a, b] lists, floats via {}), printed immediately. write adds no newline; writeln and nl add one.

Functions

plg_rt_b_nl_0

nl/0: print a newline. Always succeeds.

plg_rt_b_plus_3

plus/3: Z = X + Y over integers; any single unbound is solved for.

plg_rt_b_succ_2

succ/2: S = X + 1 over non-negative integers, both modes.

plg_rt_b_unify_with_occurs_check_2

unify_with_occurs_check/2: like =/2 but fails rather than build a cyclic term. Local iterative implementation — bindings are trailed so the caller’s choice-point rewind undoes a partial unification.

plg_rt_b_write_1

write/1: print the term (v1 term_to_string), no trailing newline.

plg_rt_b_writeln_1

writeln/1: write/1 followed by a newline.