[Maxima] [Newbie] problem with conditional expression

[Hugo Coolens]

I'm trying to define a function as follows:
f(t):= if (0<=t and t<t1) then -(A/t1)*t+A else 0;

when trying out "f(0);" I get the error message below, probably 
because the syntax I use is wrong, can someone tell me how to do it 
properly?


  MACSYMA was unable to evaluate the predicate:
0 < t1
#0: f(t=0)
  -- an error.  Quitting.  To debug this try DEBUGMODE(TRUE);