MINUS num
- num

	outputs the negative of its input.  Minus sign means unary minus if
	the previous token is an infix operator or open parenthesis, or it is
	preceded by a space and followed by a nonspace.  There is a difference
	in binding strength between the two forms:

		MINUS 3 + 4	means	-(3+4)
		- 3 + 4		means	(-3)+4