diff --git a/2022/day21.py b/2022/day21.py
new file mode 100644
index 0000000..1bf485d
--- /dev/null
+++ b/2022/day21.py
@@ -0,0 +1,74 @@
+from helpers import *
+from sympy import Symbol, Eq, solve
+
+lines = read_day(day).split('\n')
+
+sample_lines = '''
+root: pppw + sjmn
+dbpl: 5
+cczh: sllz + lgvd
+zczc: 2
+ptdq: humn - dvpt
+dvpt: 3
+lfqf: 4
+humn: 5
+ljgn: 2
+sjmn: drzm * dbpl
+sllz: 4
+pppw: cczh / lfqf
+lgvd: ljgn * ptdq
+drzm: hmdt - zczc
+hmdt: 32
+'''.strip().split('\n')
+
+monkey_re = re.compile(r'(\w{4})')
+def eval_root(lines: list[str]):
+	monkeys = {}
+	for line in lines:
+		monkey, _, operation = line.partition(': ')
+		operation = monkey_re.sub(r'e("\1")', operation)
+		# print(monkey, operation)
+		monkeys[monkey] = operation
+
+	@cache
+	def e(monkey):
+		return eval(monkeys[monkey], {'e': e})
+
+	return int(e('root'))
+
+def inline_monkeys(lines: list[str]):
+	monkeys = {}
+	for line in lines:
+		monkey, _, operation = line.partition(': ')
+		monkeys[monkey] = operation
+
+	monkeys['root'] = monkeys['root'].replace('+', '==')
+	monkeys['humn'] = 'X'
+
+	# delisp_pattern = re.compile(r'\((\d+)\)')
+	# eval_pattern = re.compile(r'\((\d+[\+\-\*\/]+\d+)\)')
+	# def ev(s):
+	# 	last = ''
+	# 	out = s.replace(' ', '').replace('/', '//')
+	# 	while last != out:
+	# 		# print('looped')
+	# 		last = out
+	# 		out = eval_pattern.sub(lambda m: str(eval(m.group(1))), last)
+	# 		out = delisp_pattern.sub(r'\1', out)
+	# 	return out.replace('//', '/')
+
+	@cache
+	def inline(monkey) -> str:
+		return monkey_re.sub(lambda m: inline(m.group(1)), f'({monkeys[monkey]})')
+	# return ev(inline('root'))
+	# lhs, _, rhs = ev(inline('root')).partition('==')
+	lhs, _, rhs = inline('root')[1:-1].partition('==')  # above leaves residual () around entire expression
+	X = Symbol('X')
+	# return solve(Eq(lhs, rhs))
+	return int(eval(f'solve(Eq({lhs}, {rhs}))')[0])
+
+
+print(f'Part 1 (sample): {eval_root(sample_lines)}')  #152
+print(f'Part 1: {eval_root(lines)}')  # 66174565793494
+print(f'Part 2 (sample): {inline_monkeys(sample_lines)}')
+print(f'Part 2: {inline_monkeys(lines)}')