BF=6; HF=2.5
p <- function(x) {f <- 0;
       for(i in 0:n) f <- f+sin((2*i+1)*x)/(2*i+1); f <- f*4/pi}
n = 0; graph1F(p, -5,10, "black")
n = 1;  graph1(p, -5,10, "blue")
n = 2;  graph1(p, -5,10, "brown")

n = 10; graph1F(p, -5,10, "seagreen")

n = 80; graph1F(p, -5,10, "red")