conversion1 : {l : Level} {t : Set l } !$\rightarrow$! (env : Env) !$\rightarrow$! {c10 :  !$\mathbb{N}$! } !$\rightarrow$! ((vari env) !$\equiv$! 0) /\ ((varn env) !$\equiv$! c10)
               !$\rightarrow$! (Code : (env1 : Env) !$\rightarrow$! (varn env1 + vari env1 !$\equiv$! c10) !$\rightarrow$! t) !$\rightarrow$! t
conversion1 env {c10} p1 next = next env proof4 where
      proof4 : varn env + vari env !$\equiv$! c10
      proof4 = let open !$\equiv$!-Reasoning  in begin
            varn env + vari env !$\equiv$!!$\langle$! cong ( !$\lambda$! n !$\rightarrow$! n + vari env ) (pi2 p1 ) !$\rangle$!
            c10 + vari env      !$\equiv$!!$\langle$! cong ( !$\lambda$! n !$\rightarrow$! c10 + n ) (pi1 p1 ) !$\rangle$!
            c10 + 0             !$\equiv$!!$\langle$! +-sym {c10} {0} !$\rangle$!
            c10
          !$\blacksquare$!