mappy.msgBox ("Merge layers", "You need to load or create a map first", mappy.MMB_OK, mappy.MMB_ICONINFO)
else
mappy.msgBox ("Merge layers", "Merges two layers, in the next dialogue enter the source layers and the destination layer separated by commas. All layers must exist, the destination can be one of the source layers. Highest block number is used. You can undo this operation with ctrl+z if destination is current layer.", mappy.MMB_OK, mappy.MMB_ICONINFO)
local isok,l1,l2,l3 = mappy.doDialogue ("Merge layers", "Enter layer1,layer2,destlayer", "0,1,0", mappy.MMB_DIALOGUE2)