#	Subtract a  piecewise-linear function from traces ('detrend')
#
#	Here, we assume that 'top' and 'bottom' are trace headers containing
#	times of two horizons. The following will subtract from trace values 
#	a function equal (constant) trace(top) above the time='top', linearly changing to 
#	trace(bottom) at time='bottom', and constant to the bottom of the trace.

*call	trcmath	
detrend		
top	=trc=
bottom	=trc=