4.5.4 Unary Adding Operators
unary adding operators + (identity) and – (negation) are predefined
for every specific numeric type T
with their conventional meaning.
They have the following specifications:
function "+"(Right : T) return T
function "-"(Right : T) return T
15 For modular integer types, the unary
adding operator –, when given a nonzero operand, returns the result
of subtracting the value of the operand from the modulus; for a zero
operand, the result is zero.