half-arch is part of:
   100%  branch
    50%  arch
    50%  tree  (indirectly)
    15%  plant  (indirectly)
     8%  flower  (indirectly)

half-arch contains:

Full expansion for half-arch:
   100%  1x3x2 Smooth-Round Half-Arch Brick
   100%  1x5x4 Staired Half-Arch Brick
   100%  1x6x2 Smooth-Round Full-Arch Brick
   100%  1x6x3 Smooth-Round Half-Arch Brick
    80%  1x4x4 Staired Half-Inverse-Arch Brick
    80%  2x3x2 DUPLO Inverse-Half-Arch Brick
    80%  2x6x2 DUPLO Dual-Inv-Half-Arch Brick
    30%  1x1x1.3 Half-Round-Top Brick w/Plate
    10%  1x4x1.3 Half-Round-Top Brick w/Plate