From 49188cbe174f6f0559037bb2f6e51300dac90a85 Mon Sep 17 00:00:00 2001
From: Scott Worley <scottworley@scottworley.com>
Date: Thu, 23 May 2019 14:37:46 -0700
Subject: [PATCH] Handle the fully-deductible case

---
 tax.js      | 3 +--
 tax.test.js | 1 +
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tax.js b/tax.js
index 7f32f74..d9bd34c 100644
--- a/tax.js
+++ b/tax.js
@@ -53,8 +53,6 @@ function merge_tax_tables(t1, t2) {
 }
 
 function invert(table) {
-  if (table.length == 0) return x => x;
-
   // Here we solve
   //   net = m * gross + b
   // for gross:
@@ -90,5 +88,6 @@ function invert(table) {
         return (net - b) / m;
       }
     }
+    return net;
   };
 }
diff --git a/tax.test.js b/tax.test.js
index 14c48c0..125cc20 100644
--- a/tax.test.js
+++ b/tax.test.js
@@ -57,5 +57,6 @@ test("invert", () => {
   assert.strictEqual(invert([                  ])(10), 10);
   assert.strictEqual(invert([[ 0, Infinity, .1]])( 9), 10);
   assert.strictEqual(invert([[10, Infinity, .1]])(19), 20);
+  assert.strictEqual(invert([[10, Infinity, .1]])( 9),  9);
   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(170), 200);
 });
-- 
2.44.1