An integration question



I don't understand how/why Maxima returns the following:

(%i3)
integrate(cos(x)-cos(x-c),x,0,c/2)=%pi-c-integrate(cos(x-c),x,c,%pi/2+c);
Is  c  positive, negative, or zero?

pos;
(%o3) 2*sin(c/2)-sin(c) = -c+sin((4*%pi*false-%pi)/2)-sin(2*%pi*false)+%pi

What is this "false" doing in the answer? In case it plays any role,
here is the build_info:

Maxima version: 5.12.99rc1
Maxima build date: 1:30 8/8/2007
host type: i686-pc-linux-gnu
lisp-implementation-type: CLISP
lisp-implementation-version: 2.41 (2006-10-13) (built 3380066971)
(memory 3395543448)

Milan
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