removes dead +mz:nl, updates +bif syntax
`+mz:nl` was determined by ~sorreg to be dead code, and there doesn't seem to be any possible `a` that will nest in the current code.
Also, `+bif:in` and `+bif:by` had the weird syntactical construct of `=<  [+< +>]`. I simplified it to the more straightforward `=< +`.
~/ %bif
|* b/*
^+ [l=a r=a]
- =< [+< +>]
+ =< +
|- ^+ a
?~ a
[b ~ ~]
~/ %bif
|* {b/* c/*}
^+ [l=a r=a]
- =< [+< +>]
+ =< +
|- ^+ a
?~ a
[[b c] ~ ~]
=> .(a ^+((le a) a))
(~(gas by `(map _p.i.-.a _q.i.-.a)`~) a)
:: ::
- ++ mz :: construct map
- |* a/(list (pair))
- => .(a ^+((le a) a))
- (~(gas by ~) a)
- :: ::
++ si :: construct set
|* a/(list)
=> .(a ^+((le a) a))
