more efficient Markup_Tree, based on branches sorted by quasi-order;
renamed markup_node.scala to markup_tree.scala and classes/objects accordingly;
Position.Range: produce actual Text.Range;
Symbol.Index.decode: convert 1-based Isabelle offsets here;
added static Command.range;
simplified Command.markup;
Document_Model.token_marker: flatten markup at most once;
tuned;
BoolNat = Arith +
types bool,nat 0
arities bool,nat :: arith
consts Suc :: "nat=>nat"
rules add0 "0 + n = n::nat"
addS "Suc(m)+n = Suc(m+n)"
nat1 "1 = Suc(0)"
or0l "0 + x = x::bool"
or0r "x + 0 = x::bool"
or1l "1 + x = 1::bool"
or1r "x + 1 = 1::bool"
end