These infix operators are used to specify edges in
caugi(). This function helps build infix operators.
.edge_spec(from_sym, to_expr, glyph)A data.table with columns from, to, and edge.
A symbol representing the source node.
An expression representing the target node(s).
Can be a symbol, string, number, c(...), or a combination using +.
A string representing the edge glyph (e.g., "-->", "<->").