model S {
    flow f from Ba.ra to HS.pa, HS.pb;
    block Ba(pa : in float, pb : in float, ra : out float [ 2 ] );
    system HS(pa : in float [ 2 ], ra : out float, pb : in float [ 2 ] , rb : out float [ 2 ] ) {
           block Bb(ra : out float, pa : in float);
           flow fa from pa to Bb.pa;
           flow fb from pb to rb;
    }
    flow fb from HS.ra to Ba.pa, Ba.pb;
    flow fc from HS.rb to;
}