function r=intl(a,b,z0,r,f)
//If f is a complex-valued function, intl(a,b,z0,r,f) computes
//the integral of f(z)dz along the complex plane curve defined by 
//  z0 + r.exp(%i*t) 
//for a<=t<=b .
//(part of the circle with center z0 and radius r with phase between a and b)
//!
//Author F.D.
//First compile f if necessary:
// Copyright INRIA
if type(f)==11 then comp(f),end;
//Define two functions for the real part and
//imaginary part of f(g(t))*g'(t) where g(t) is a 
//parametrization of the circle.
deff('y=real1(t)','z=z0+r*exp(%i*((1-t)*a+t*b)),...
y=real(f(z)*%i*(b-a)*z)')
deff('y=imag1(t)','z=z0+r*exp(%i*((1-t)*a+t*b)),...
y=imag(f(z)*%i*(b-a)*z)')
r=intg(0,1,real1)+%i*intg(0,1,imag1)