The logic constants are the integer constants TRUE and FALSE. While the constant TRUE has the value 1, in general any integer value different to 0 will serve as a truth value of true (see Boolean).
TRUE and FALSE are special in that, unlike all other constants, neither of them can be prefixed by a minus sign in either the globals section or after a typecast, for example:
integer a = -TRUE; // Syntax error integer b = -LINK_ROOT; // Valid default { state_entry() { integer c = (integer)-FALSE; // Syntax error integer d = (integer)-LINK_ROOT; // Valid } }