From card no. 3P3VFGYR:

what does that signify? the rackets. b
what does that signify? the rackets. b T(h) is f(x) or function notation. T or f are the rule, h or x is the input into the T or f machine ... h - m xx xxxxx h into T gives you T(h) x into f gives you f(x) pronounced T of h or f of x