A=a(b(c(d,d),c(d,d)),b(c(d,d),c(d,d)))?
print_depth(0)?
print_depth(1)?
print_depth(2)?
print_depth(3)?

A=`(1+2+3+4+5+6)?
print_depth(0)?
print_depth(1)?
print_depth(2)?
print_depth(3)?
print_depth(4)?
print_depth(5)?
print_depth(6)?
print_depth(7)?
print_depth(8)?

print_depth(0)?
print_depth(-1)?
print_depth(3)?
print_depth(-1)?

A=s(X,t(X:u(v)))?
print_depth(0)?
print_depth(1)?
print_depth(2)?

A=s(t(X),X:u(v(w)))?
print_depth(0)?
print_depth(1)?
print_depth(2)?
print_depth(3)?

A=X:w(w(w(X)))?
print_depth(0)?
print_depth(1)?
print_depth(2)?
print_depth(3)?

