confusing code

[argman]

local ResidualUp = n >= 2 and ResidualPyramid or Residual

as i am not familar with lua, what does this mean ? if n >=2 use res_pyra and others residual? but the parameters of the two function is not the same

[xiashh]

If n >= 2, then ResidualUp = ResidualPyramid Else, ResidualUp = Residual