Top Cover， Bottom Cover， And Cover Board
concave downward‘ concave down
concave-up concave-down
plane-concave lens (=plano-concave lens)
cover-to-cover translation
with average cover {= WA Cover}
0-diagonally concave relation
Abney mounting for concave grating
absolutely concave function
An are equi-uniformly u0-concave operators
annular concave spherical surface
belt conveyor + concave segment + curvature radius
blade with concave surface
central concave abrasive
characteristic concave or convex of surface