EAS curve (EAS standing for equilibrium aggregate supply) is a vertical
line in a diagram with inflation on the vertical axis and with income
on the horizontal axis. It indicates how much output firms produce
at different inflation rates, given that firms and workers (or unions)
anticipated this rate of inflation correctly.
The EAS curve being vertical means that properly anticipated inflation
does not bear on production. Output is always at potential output
Y*, no matter how high inflation is. The reason is that with inflation
being as anticipated, the real wage is exactly where it clears the
labour market. Inflation that trade unions did foresee only affects
nominal wages, but not real wages. Thus it also does not affect
employment, and it does not affect output produced.
Further reading on pp. 196-167.