Add new theorems and proofs

EasyLean.lean

@@ -1 +1,2 @@
 import EasyLean.Basic
+import EasyLean.Mathd.Algebra.MathdAlgebra513

EasyLean/Basic.lean

@@ -1,12 +1,5 @@
 import Mathlib.Data.Real.Basic
 import Mathlib.Tactic.Linarith
 
-theorem mathd_algebra_513
-  (a b : ℝ)
-  (h₀ : 3 * a + 2 * b = 5)
-  (h₁ : a + b = 2) :
-  a = 1 ∧ b = 1 := by
-  sorry
-
 theorem eq_four : ∀ a b c d : Nat, a = b → a = d → a = c → c = b := by
   sorry

EasyLean/Mathd/Algebra/MathdAlgebra513.lean

@@ -0,0 +1,19 @@
+import Mathlib
+
+namespace EasyLean
+
+namespace Mathd
+
+namespace Algebra
+
+theorem mathd_algebra_513 (a b : ℝ)
+    (h₀ : 3 * a + 2 * b = 5)
+    (h₁ : a + b = 2) :
+    a = 1 ∧ b = 1 := by
+  constructor <;> linarith [h₀, h₁]
+
+end Algebra
+
+end Mathd
+
+end EasyLean