Ticket #2919: addaa.py

if len(session.models) == 0:
    from chimerax.core.commands import run
    run(session, "open 3fhr")
s = session.models[0]
for r in s.residues:
        if r.chain_id == "A" and r.number == 217:
                break
r = s.new_residue("THR", "A", 195, precedes=r)
from tinyarray import array as crd
from chimerax.atomic.struct_edit import add_atom, add_bond
c = add_atom("C", "C", r, crd([0,0,4]))
ca = add_atom("CA", "C", r, crd([0,0,2]), bonded_to=c)
n = add_atom("N", "N", r, crd([0,0,0]), bonded_to=ca)
for r in s.residues:
        if r.chain_id == "A" and r.number == 194:
                break
add_bond(r.find_atom("C"), n)