Squire transformation
= Squire transformation
{c}
{title2=$k'=\sqrt{k^2+l^2},\quad R'=kR/k',\quad c'=c$}
For positive streamwise <wavenumber> $k$, replace a three-dimensional <Orr-Sommerfeld equation> by a two-dimensional one with the displayed parameters. Both the transverse operator and the coefficient $1/(ikR)$ remain unchanged, preserving the eigenfunction and phase-speed <eigenvalue>. This proves the modal comparison in <Squire's theorem>.