The formula

(frequency) = (speed of light)/(wavelength)

says that a frequency shift entails either a wavelength shift or a speed-of-light shift.

If the speed of light is invariable, as Einstein postulated in 1905, the implication is

"Any frequency shift entails a wavelength shift".

This implication is almost obviously false (easy to imagine a counterexample), so the underlying axiom "The speed of light is invariable" is false as well.

If the wavelength of light is invariable, as future physics will have to postulate, the implication is

"Any frequency shift entails (is caused by) a speed-of-light shift".

Pentcho Valev