[asterisk-users] MATH function

[Rilawich Ango]

I try to use function MATH or GoToIf for checking the negative value
but CLI shows an error as following.

exten => s,11,Set(bt=${MATH(-1>0)})
func_math.c:164 builtin_function_math: '' is not a valid number

exten => s,11,GoToIf($[-1 < 0]?20)
WARNING[12926]: ast_expr2.y:729 op_negate: non-numeric argument

It seems both functions can't accept negative number for comparison.
What function can I use to compare negative number?