Syntax: CONNECT pexpr pexpr [ IF (expr) ]

   (`Pexpr' is the name of a vector, or an expression in parentheses,
e.g. CONNECT x (sqrt(y)) if(y > 0) )

   CONNECT draws line segments connecting the points in vectors pexpr1
and pexpr2. If the IF clause is present, it only connects those points
for which expr (see ARITHMETIC and LOGICAL) is non-zero.