interpretation string: de.up.ling.irtg.algebra.StringAlgebra
interpretation ref: de.up.ling.irtg.algebra.SetAlgebra
interpretation sem: de.up.ling.irtg.algebra.SubsetAlgebra

// a referent is always the location the current subtree refers to
// Terminalsymbole dürfen nur in einer einzigen Regel auftreten

S! -> s(RefLoc)
  [string] *("put the block", ?1)
  [ref] ?1
  [sem] ?1 

RefBlock -> blockloc(RefLoc)
  [string] *("the block", ?1)
  [ref] ?1
  [sem] ?1

// RefLoc - refers to a position which may or may not contain a block

RefLoc -> top(RefBlock)
  [string] *("on top of", ?1)
  [ref] project_1(intersect_2(top-of,?1))
  [sem] ?1
  
RefLoc -> below(RefBlock)
  [string] *("below of", ?1)
  [ref] project_2(intersect_1(top-of,?1))
  [sem] ?1
  
RefLoc -> left(RefBlock)
  [string] *("to the left of", ?1)
  [ref] project_1(intersect_2(left-of,?1))
  [sem] ?1
  
RefLoc -> right(RefBlock)
  [string] *("to the right of", ?1)
  [ref] project_2(intersect_1(left-of,?1))
  [sem] ?1
  
RefLoc -> front(RefBlock)
  [string] *("infront of", ?1)
  [ref] project_1(intersect_2(in-front-of,?1))
  [sem] ?1
  
RefLoc -> behind(RefBlock)
  [string] *("behind of", ?1)
  [ref] project_2(intersect_1(in-front-of,?1))
  [sem] ?1
  

RefBlock -> uniqblockdesc(AdjBlock)
 [string] *("the", ?1)
 [ref] project_2(intersect_1(at, size_1(?1)))
 [sem] ?1

AdjBlock -> orangeblock
  [string] "orange block"
  [ref] orange
  [sem] EMPTYSET
  
AdjBlock -> yellowblock
  [string] "yellow block"
  [ref] yellow
  [sem] EMPTYSET

AdjBlock -> blueblock
  [string] "blue block"
  [ref] blue
  [sem] EMPTYSET

AdjBlock -> prevblock
  [string] "previous block"
  [ref] it
  [sem] EMPTYSET