diff --git a/package.json5 b/package.json5
index a0cd6c3..b6575a1 100644
--- a/package.json5
+++ b/package.json5
@@ -7,7 +7,7 @@
       test: 'echo "Error: no test specified" && exit 1',
       build: 'mkdirp build && cpy etc/package.json build --flat && tsc',
       start: 'node build',
-      go: 'pnpm --sequential "/build|start/"',
+      go: 'pnpm --sequential "/clean|build|start/"',
       clean: 'del-cli build',
    },
    packageManager: 'pnpm',
diff --git a/src/index.ts b/src/index.ts
index 8b4ecfd..dc389e8 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -8,17 +8,30 @@ import {absquare as absquare_complex} from './Complex/arithmetic.js'
 
 const mockRealAdd = (a: number, b: number) => a+b
 const mockComplexAbsquare = (z: Complex<number>) => z.re*z.re + z.im*z.im
+const mockComplex = (re: number, im: number) => ({ re, im })
+
+const config = {
+  predictable: false,
+  epsilon: 1e-14
+}
 
 const quatAbsquare = absquare_complex({
-    add: mockRealAdd,
-    absquare: mockComplexAbsquare
+  add: mockRealAdd,
+  absquare: mockComplexAbsquare
 })
 
 const myabs = quatAbsquare({re: {re: 0, im: 1}, im: {re:2, im: 3}})
 const typeTest: typeof myabs = 7 // check myabs is just a number
+console.log('Result is myabs=', myabs)
 
-console.log('Result is', myabs)
+const sqrt = Specifications.numbers.sqrt({
+  config,
+  complex: mockComplex
+})
+console.log('Result of sqrt(16)=', sqrt(16))
+console.log('Result of sqrt(-4)=', sqrt(-4))
 
 // Check type of the generic square implementation
+console.log('Type of sqrt (number) is', Specifications.numbers.sqrt.reflectedType)
 console.log('Type of square is', Specifications.generic.square.reflectedType)
 console.log('Type of complex square root is', Specifications.complex.sqrt.reflectedType)
diff --git a/src/numbers/arithmetic.ts b/src/numbers/arithmetic.ts
index 11da5c2..d2d3414 100644
--- a/src/numbers/arithmetic.ts
+++ b/src/numbers/arithmetic.ts
@@ -1,5 +1,6 @@
 import type {configDependency} from '../core/Config.js'
 import type {Dependencies, Signature} from '../interfaces/type.js'
+import { $implement } from '../interfaces/type.js'
 
 export const add:        Signature<'add',        number> = (a, b) => a + b
 export const unaryMinus: Signature<'unaryMinus', number> = a => -a
@@ -13,13 +14,14 @@ export const divide:     Signature<'divide',     number> = (a, b) => a / b
 const basicSqrt = a => isNaN(a) ? NaN : Math.sqrt(a)
 export const conservativeSqrt: Signature<'conservativeSqrt', number> = basicSqrt
 
-export const sqrt =
-   (dep: configDependency & Dependencies<'complex', number>):
-   Signature<'sqrt', number> => {
-      if (dep.config.predictable || !dep.complex) return basicSqrt
-      return a => {
-         if (isNaN(a)) return NaN
-         if (a >= 0) return Math.sqrt(a)
-         return dep.complex(0, Math.sqrt(unaryMinus(a)))
-      }
-   }
+$implement!('sqrt',
+  (dep: configDependency & Dependencies<'complex', number>): Signature<'sqrt', number> => {
+    if (dep.config.predictable || !dep.complex) {
+      return basicSqrt
+    }
+    return a => {
+      if (isNaN(a)) return NaN
+      if (a >= 0) return Math.sqrt(a)
+      return dep.complex(0, Math.sqrt(unaryMinus(a)))
+    }
+  })