  We derive stringent constraints on neutrino speed, weak equivalence principle
violation, Lorentz invariance violation, and dual lensing from the first
high-energy astrophysical neutrino source: TXS 0506+056. Observation of
neutrino (IceCube-170922A) and photons in a similar time frame and from the
same direction is used to derive these limits. We describe ways in which these
constraints can be further improved by orders of magnitude.
