diff --git a/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/Evaluator.kt b/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/Evaluator.kt
index f47e46bf..07ad1528 100644
--- a/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/Evaluator.kt
+++ b/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/Evaluator.kt
@@ -1,9 +1,10 @@
 package ch.kleis.lcaac.core.lang.evaluator
 
 import ch.kleis.lcaac.core.lang.SymbolTable
-import ch.kleis.lcaac.core.lang.evaluator.protocol.Oracle
 import ch.kleis.lcaac.core.lang.evaluator.protocol.Learner
+import ch.kleis.lcaac.core.lang.evaluator.protocol.Oracle
 import ch.kleis.lcaac.core.lang.expression.*
+import ch.kleis.lcaac.core.lang.register.ProcessKey
 import ch.kleis.lcaac.core.math.QuantityOperations
 import org.slf4j.LoggerFactory
 
@@ -32,9 +33,23 @@ class Evaluator<Q>(
         }
     }
 
-    fun trace(template: EProcessTemplate<Q>, arguments: Map<String, DataExpression<Q>> = emptyMap()): EvaluationTrace<Q> {
-        return prepareRequests(template, arguments)
-            .let(this::trace)
+    fun with(template: EProcessTemplate<Q>): Evaluator<Q> {
+        val processKey = ProcessKey(template.body.name)
+        if (symbolTable.processTemplates[processKey] != null) throw IllegalStateException("Process ${template.body.name} already exists")
+        val st = this.symbolTable.copy(
+                processTemplates = this.symbolTable.processTemplates.plus(
+                    mapOf(processKey to template)
+                )
+            )
+        return Evaluator(st, ops)
+    }
+
+    fun trace(
+        template: EProcessTemplate<Q>,
+        arguments: Map<String, DataExpression<Q>> = emptyMap()
+    ): EvaluationTrace<Q> {
+        val requests = prepareRequests(template, arguments)
+        return trace(requests)
     }
 
     private fun <Q> prepareRequests(
diff --git a/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/EvaluatorTest.kt b/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/EvaluatorTest.kt
index b4e48924..f24610a6 100644
--- a/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/EvaluatorTest.kt
+++ b/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/EvaluatorTest.kt
@@ -13,6 +13,7 @@ import ch.kleis.lcaac.core.math.basic.BasicNumber
 import ch.kleis.lcaac.core.math.basic.BasicOperations
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.Timeout
+import org.junit.jupiter.api.assertThrows
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
 import kotlin.test.assertNotEquals
@@ -20,6 +21,60 @@ import kotlin.test.assertNotEquals
 class EvaluatorTest {
     private val ops = BasicOperations
 
+    @Test
+    fun with_whenNewTemplate() {
+        // given
+        val template = EProcessTemplate(
+            body = EProcess(
+                name = "eProcess",
+                products = listOf(
+                    ETechnoExchange(QuantityFixture.oneKilogram, ProductFixture.carrot)
+                ),
+                impacts = listOf(
+                    ImpactFixture.oneClimateChange
+                ),
+            )
+        )
+        val evaluator = Evaluator(SymbolTable.empty(), BasicOperations)
+            .with(template)
+        val expected = ImpactValue(
+            QuantityValueFixture.oneKilogram,
+            IndicatorValueFixture.climateChange,
+        )
+
+        // when
+        val actual = evaluator.trace(template).getEntryPoint().impacts.first()
+
+        // then
+        assertEquals(expected, actual)
+    }
+
+    @Test
+    fun with_whenNameCollision_shouldThrow() {
+        // given
+        val template = EProcessTemplate(
+            body = EProcess(
+                name = "eProcess",
+                products = listOf(
+                    ETechnoExchange(QuantityFixture.oneKilogram, ProductFixture.carrot)
+                ),
+                impacts = listOf(
+                    ImpactFixture.oneClimateChange
+                ),
+            )
+        )
+        val symbolTable = SymbolTable(
+            processTemplates = ProcessTemplateRegister.from(mapOf(
+                ProcessKey("eProcess") to template
+            ))
+        )
+        val evaluator = Evaluator(symbolTable, BasicOperations)
+
+        // when/then
+        val e = assertThrows<IllegalStateException> { evaluator.with(template) }
+        assertEquals("Process eProcess already exists", e.message)
+    }
+
     @Test
     fun eval_processWithImpacts_shouldReduceImpacts() {
         // given