Using first function

I need to code the following. Merge temp1, temp_b and temp_wldr by id. If multi=1 then do; if rel=0 then whldr =1; else whldr=0;end; else if multi>1 and b >=1 then do; if rel =0 and a=1 then whldr=1; else whldr=0;end; else if multi>1 and b=0 then whldr=1 for the first person with rel=0 and a ne 0;else whldr=0.