reverse_interface_mapping : bool ref
# reverse_interface_mapping := true;; val it : unit = () # REAL_EQ_SUB_LADD;; val it : thm = |- !x y z. x = y - z <=> x + z = y
# reverse_interface_mapping := false;; val it : unit = () # REAL_EQ_SUB_LADD;; val it : thm = |- !x y z. (x = real_sub y z) = real_add x z = y