added groups

src/utils.typ

@@ -0,0 +1,27 @@
+#let get-participants-i(participants) = {
+  let pars-i = (:)
+  for (i, p) in participants.enumerate() {
+    pars-i.insert(p.name, i)
+  }
+  return pars-i
+}
+
+#let get-group-span(participants, group) = {
+  let min-i = participants.len() - 1
+  let max-i = 0
+  let pars-i = get-participants-i(participants)
+
+  for elmt in group.elmts {
+    if elmt.type == "seq" {
+      let i1 = pars-i.at(elmt.p1)
+      let i2 = pars-i.at(elmt.p2)
+      min-i = calc.min(min-i, i1, i2)
+      max-i = calc.max(max-i, i1, i2)
+    } else if elmt.type == "grp" {
+      let (i0, i1) = get-group-span(participants, elmt)
+      min-i = calc.min(min-i, i0)
+      max-i = calc.max(max-i, i1)
+    }
+  }
+  return (min-i, max-i)
+}