Question: How do I merge two functions into one

Hi to all

I am trying to merge two functions into a single graph. I have discovered the "piecewise" function but however I want to be able to manipulate the variables in both functions and plot a 3D graph to determine the results.

this is what I have so far

Z := proc (t)

if subs(p = 25, (100-p)*(1-exp((-1)*.11*t))/(10.00000000*exp((-1)*.11*t)+1)) < CM and 0 < t then subs(p = 25, (100-p)*(1-exp((-1)*.11*t))/(10.00000000*exp((-1)*.11*t)+1))

else

subs(gamma = .1, p = 50, (-100+p)*(1-exp((-1)*.11*t))/((-1+gamma)*(10.00000000*exp((-1)*.11*t)+1)))

end if

end proc

The problems that I have been experencing is that, in the procedures, the globally declared variables cannot be recongnized and because of this I cannot set a range for the variables to run the procedure.

Your help is appreciated