lookup()

Syntax: lookup(x,a1,a2,b1,b2,…,c1,c2)

Arguments:
x: a numeric expression
a1,a2,b1,b2,…c1,c2 is a list of pairs of values.

Return value: The value of the second value of the pair whose first value is less than or equal to x.

The list of value pairs must be sorted on the first value of each pair.